The present invention relates to techniques for communicating primary and secondary data streams over a communication channel.
It is often desirable in data communications applications to transmit not only principal, or primary, data, but also secondary data. For example, present-day voiceband data sets, or modems--particularly those designed for private-line operation--are often arranged to not only transmit the so-called user's data, but also diagnostic and/or maintenance data via which the data sets themselves communicate.
Conventionally, the available transmission bandwidth is divided into so-called primary and secondary channels in which the primary and secondary data are respectively transmitted. Depending, however, on the desired primary data transmission speed and the expected quality of the transmission channel, the primary channel bandwidth requirements may be such as to preclude this approach because every Hertz of bandwidth may be needed for the primary channel.